Electronic Structure of Homo-phase Grain Boundaries and Correlated Percolation -Fundamental Understanding of Transport Property and Nano-scale Microstructure Control of Composite Superconductors-

1.样品制备及微观结构观察：为了弄清织构程度，在织构的Ag衬底上制备了Bi2223多晶薄膜。用EBSP研究了晶界取向，用扫描电子显微镜和电子探针分析了晶界的微观结构特征。建立了1微米[0011]取向Bi2223薄膜的晶体生长工艺。2.临界电流的测量与分析：利用图案化样品在微区研究了Bi2223薄膜的电流-电压关系。精确测量了Y123薄膜的磁场角度依赖关系和应变依赖关系。测量了Bi2223薄膜的临界电流与温度的关系。他们的实验数据被应用于威布尔分析。研制出了77K下临界电流密度大于1 mA/m2的高性能Bi2223薄膜。3.…用弱连接路径模型进一步分析了Bi2223带材的临界电流：根据该模型估算了样品中的最佳渗流路径。将计算机模拟得到的J-E曲线与实验数据进行了比较。通过比较，阐明了(A)电流集中、(B)非Sc键聚集、(C)非Sc团簇分布等微观结构因素。4.基于弱连接路径模型的多晶样品输运特性的改善：从基于该模型的理论计算中考虑了输运特性的优化。提出了Bi2223带材实现最佳性能的微观组织模型，其中晶界薄弱环节限制了临界电流。5.Bi2223带材的力学性能及其对临界电流的影响：基于混合法则，考虑热残余应力，分析了Bi2223带材的力学性能。明确了施加在Sc氧化层上的真实应力。在高达60 Mpa的应力区，临界电流随应力的增加而可逆地减小。这一现象归因于同相晶界弱连接的SnS结。较少

1.Sample preparation and microstructure observation : in order to make clear the degree of texturing, the polycrystalline Bi2223 films were prepared on the textured Ag substrate, Mg0 or SrTi03 single crystal. The crystal orientation was investigated by means of EBSP and the microstructural features of grain boundaries have been precisely analyzed by using SEM and EPMA. The crystal growth technique to prepare the [0011 oriented Bi2223 film with 1 micron-meter was established.2.Measurement and analysis of critical currents : the current - voltage relationship has been investigated at the micro-area by using the patterned samples. Its angular dependence of magnetic field and the strain dependence in Y123 thin films were precisely measured. The temperature dependence of critical current was measured in Bi2223 films. Their experimental data were applied to Weibull analysis. The high performance Bi2223 thin film with critical current density higher than 1 MA/m2 at 77 K has been developed.3.A … More nalysis of critical current of Bi2223 tape by using Weak Link Path model : the optimum percolation path in the sample has been estimated based on the model. The J-E curve obtained by computer simulation was compared with the experimental data. From the comparison, some microstructure factors like (a) current concentration, (b) clustering of non-SC links, (c) distribution of non-SC clusters have been elucidated.4.Improvement of transport property in the polycrystalline samples based on the Weak Link Path model : the optimization of transport properties was considered from the theoretical calculation based on the model. As a result, the microstructure model to realized the optimum property in Bi2223 tapes was proposed, where the grain boundary weak link limits the critical current.5.Mechanical property and its influence to critical current in Bi2223 tapes : the mechanical property of Bi2223 tapes was analyzed based on the rule of mixture by taking into consideration about the thermal residual stress. The true stress exerted on the SC oxide layer was made clear. In the stress region up to 60 MPa, the critical current reversibly decreased with increasing stress. This phenomenon was attributed to the SNS junction of the weak link at homo-phase grain boundaries. Less